The present invention relates to a radio transmitter and receiver device having a head band, one end of which is provided with a transmitting microphone and the other end provided with a receiving speaker, and more specifically to a radio transmitter and receiver device in which the transmitting microphone of a bone transmission type is employed so that a clear communication of radio conversation may be accomplished without picking up noises from the transmitting side.
For conversation between a plurality of persons who are at remote locations from each other, for example, at sites of construction work, places of work and group activities in schools, transceivers of a hand-free voice control type are widely used. Also, for conversation between a specific student and a teacher through a master unit and a daughter unit of a studying apparatus for foreign language, a transmitter and receiver device in which a speaker and a microphone are mounted on a head band is used as such apparatus.
The transmitter and receiver device in which a speaker and a microphone are integrally mounted on a head band is disclosed, for example, in U.S. Pat. No. 4,138,598. The transmitter and receiver device in said U.S. Patent has a speaker placed in contact with both ends of a head band so as to block the ears, and the other end of a bar having a microphone mounted on one end thereof is pivotably mounted on one end of the head band. In such a transmitter and receiver device, voice sounds emitted from the user's mouth and all kinds of noises resulting from external environments, for example, noises generated from architectural machines and the like, enter the microphone. As a consequence, a person who receives the voice input receives voice sounds which contain; these noises thereby making it difficult to discriminate the voice sounds. That is, one receives voice sounds which are poor in SN (signal-to noise) ratio thereby causing listener fatigue. Therefore, for example, in the site of work where industrial machines and civil engineering machines are driven, there has been posed a problem in that such a transmitter and receiver device fails to achieve good function in business conversation. In a transceiver using such a transmitter and receiver device, there has been posed a problem in that the above-described noises cause switching control of transmitting and receiving to make mistake, failing to make conversation. In other words, there has been a problem in that in the transmitter and receiver device which performs transmitting and receiving, receiving becomes impossible by deterioration of the ratio of voice sounds to noise sounds on the transmitter side.
In order to improve these disadvantages, a so-called bone transmission type microphone, which detects a voice oscillation of an external auditory canal transmitted through bone tissue of a head from the mouth, has been recently developed. Such a bone transmission type microphone is disclosed, for example, in U.S. Pat. No. 4,150,262. The bone transmission type microphone comprises a casing having an insert inserted into an external auditory canal, a retainer secured within said casing, a piezo-electric element having one end secured to said retainer and the other end positioned within the insert, and a lead wire for providing a polarization voltage from the piezo-electric element. With this structure, the oscillation of the external auditory canal generated when a voice sound is emitted is transmitted to the piezo-electric element, and the polarization voltage may be obtained through the lead wire from the piezo-electric element in accordance with the generation of strain as the result of said oscillation. This voltage is again regenerated as voice through an amplifier or the like, and subjected to necessary correction of voice, which is put out to the speaker to catch the voice. Thus, only clear voice can be received without introducing external noises into the microphone together with the aural signal.
If such a bone transmission type microphone is incorporated into the transmitter and receiver together with a head phone as described above, both the left and right ear holes are blocked by the head phone and microphone, respectively. If this device is used at the site of construction work, external alarm, noises of movement of machines or the like do not directly enter the ears, and this poses a very dangerous condition.